The present invention relates to a device that can be used to indicate the pressure that existed within a pressure vessel just prior to its being opened. More particularly, the present invention is useful in occupant safety restraint systems employing hybrid inflators.
Hybrid inflators typically include a pressure vessel having a quantity of stored gas under pressure. If such an inflator, after being installed in a vehicle, leaked during its useful product life, there may not be sufficient pressurized gas therein to adequately inflate an air bag. Some hybrid inflators include a low pressure switch to generate a warning signal to the driver, in the event that a determinable quantity of gas has leaked out of the inflator. The low pressure switch is connected with electronic circuitry to enable a warning indicator such as a light in the instrument panel. The pressure sensor signal indicates that the inflator may not be in an operative condition and that repair or replacement may be needed. History and experience have shown that the use of a low pressure switch is unnecessary. Pressure sensors include wires which extend through openings in the pressure vessel. These openings are appropriately sealed using a glass to metal seal of known variety. As can be appreciated these wires create a potential leak path if they are not correctly sealed. The low pressure switch, and its corresponding circuitry or electronic signal conditioning unit, are used also to provide an electronic record such as storing a coded message on a memory chip, to determine whether or not a pressure sensor signal was generated as an indication that the inflator was or was not properly functioning prior to an accident. If the pressure sensor is eliminated there is still a need to show that the hybrid inflator was properly pressurized prior to an accident and contained a sufficient amount of pressurized gas to inflate an air bag.
It is the object of the present invention to provide a device for use within the hybrid inflator that will provide a post depressurization, or "tell tale", indication that the inflator functioned properly. An additional object of the present invention, is to provide an hybrid inflator having a higher degree of reliability against leakage than one that includes a pressure switch.
Accordingly, the invention comprises: a) storing the fluid in a member at the pressure level that existed in the pressure vessel prior to depressurization, b) providing in the member a part sensitive to the pressure differential thereacross, the pressure differential comprising the pressure in the member and the pressure in the pressure vessel, c) causing the member to move in response to the pressure differential generated upon depressurization to provide a permanent indication of the pressure stored in the member. More specifically, the device comprises: first means capable of one of rupturing, moving or deforming in to response a pressure differential thereacross above a low limit value and for providing an indication of the pressure within the pressure vessel just prior to its being opened, and support means within the pressure vessel for supporting the first means. Various embodiments of the device are provided.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.